1. Field of the Invention
The present invention relates to the detection of adequate transversal and longitudinal seals for packaging composed of a laminated material. Specifically, the present invention relates to a method to determine if the transversal and longitudinal seals of a parallelepiped container fabricated on a vertical form, fill and seal packaging machine, and a material therefor.
2. Description of the Related Art
During fabrication of the ubiquitous TETRA BRIK.RTM. package or imitators thereof, on a vertical form fill and seal machine, transversal and longitudinal seals are made to a web of material to create the general form of the package. Further folding and sealing of the flaps creates the distinctive TETRA BRIK.RTM. package. The package is usually composed of a paperboard base layer with a barrier layer such as aluminum and coatings of a thermoplastic such as polyethylene. During production, it is recommended that the operator verify the seals of at least one package every predetermined time period. For example, if the production time is six hours, the operator should verify the seals every thirty minutes.
The operator verifies the seal by tearing open the package at its seal, essentially attempting to "unseal" the package. Thus, to verify a transversal seal, the operator grasps each side of the package and exerts an outward force to tear open the package. If the transversal seal is adequate, delamination will occur, the paperboard layer will rupture, or the aluminum layer will come off of one side of the sealing area. However, if the seal is inadequate the two sides will separate without rupturing. The operator is sometimes unable to distinguish between a delaminated sealing area and one in which the two sides have separated without rupturing. When this occurs, the entire production will be mistakenly destroyed by the operator under the belief that the transversal seal is inadequate, thereby possibly rendering the product defective. It is obvious that such a mistake may increase the costs of production.
A similar verification of the longitudinal seal is also performed at set intervals during a production cycle. However the longitudinal seal involves a strip that is sealed to the web of packaging material to create a tube about the fill pipe of the packaging machine. An operator determines if the strip is adequate by tearing the strip from the package. The seal is defective if the strip is removed without affecting the thermoplastic coatings. However, the longitudinal strip is also a laminated material and confusion between delamination and unaffected coatings may lead the mistaken belief that the seal is inadequate.
Thus, there remains a need to clearly determine if the transversal and longitudinal seals are acceptable or defective.